[Elecraft] Filter Calibrate Question

[John Huffman]

Once again the mysteries of filter calibration escape me.

Looking at Spectrogram, I see that my CW filters are close.  I use OPT1,
1000, 500, 250.  A tone at 600Hz on OPT1 is at that same place +/- 20 Hz.
for each of the other filters.

Sideband is different.  I noticed last night that in filters 3 and 4 that
the LSB signal moved and I have to tune about 100 Hz. lower to tune it in.
To check, I tuned in, on LSB, the audio tone from my Fort Smith QRP Group
Frequency standard to 600 Hz..  (The same holds for USB, but in the opposite
direction.)

Filter                Tone      BFO Freq.
Filter 1 OPT1 - 600 - 4913.58
Filter 2 OPT1 - 603 - 4913.47
Filter 3 OPT1 - 680 - 4913.33
Filter 4 1.60 KHz. - 684 - 4913.00

As you can see, filters 3 and 4 move the tone, that is, change the received
frequency.  I didn't know the filter could change receive frequencies.

Anyway, I played with the BFO settings and in the end returned near the
original settings, but now the tones line up fine at 600 HZ +/- 20 Hz.  Dumb
luck?

So, how does changing filters result in a change of frequency?  How does one
fix this other than resetting the BFO frequencies to where they had been?
Why can't I get all the filters to receive signals on exactly the same
frequency?

Thanks in advance...

73 de NA8M
John